The invention relates to a method for producing a fork arm for load-carrying devices, said fork arm comprising a fork blade which is substantially horizontal in the operating position, and a substantially vertical fork back that connects via a fork bend to said fork blade and is provided with connection elements for the conveying device, wherein the fork arm consists of a plurality of parts that are connected to one another, and at least a number of said parts are welded together.
The invention also relates to a fork arm produced according to this method.
A known fork arm is disclosed in DD 256 050 A3 and is shown and described there in the sole exemplary embodiment as consisting of three steel lamellas welded together at the edge by means of a fillet weld, wherein it is mentioned that the individual lamellas can be adhesively bonded to one another, but without suggesting a manner in which adhesive bonding can be carried out. The outer lamellas can be made here from quality steel, and the inner lamella can be made of conventional construction steel. With the described configuration, the complexity during the production is to be reduced since the individual lamellas can be produced by bending and without forging.
This known approach could indeed simplify the production; however, the strength of the fork arm cannot be achieved by the steel lamellas that are welded together at the edge by fillet welds, and, in particular, because of the lateral welding using fillet welds, the deflection of the fork arm under load is significantly greater than that of conventional fork arms made of heat treatable steel. Furthermore, the lamella thickness has been selected such that bending the fork bend has to be carried by locally heating the bending area, and energy supply is already very high during bending. A second additional increased energy supply takes place through the selected welding method using fillet welds at the edge of the steel lamellas, wherein a third further energy supply is required for stress relief annealing the welds.
For simplifying the production, it also became known from DE 195 834 C1 to fabricate the fork blade and/or the fork back or even the whole fork arm from plates that are arranged side by side and are welded together at some places. Through this, forging work can be avoided at least to a certain extent; however, welding at certain areas is complicated and critical work, which overall is detrimental to the strength of the entire fork arm.
The document EP 0 560 524 A1 likewise shows a fork arm consisting of lamellas, wherein all possibilities of connecting lamellas of a fork arm are left open; however, in particular adhesive bonding is discussed and also welding is discussed in general form, wherein as the sole example, weld beads 52 are described and shown in FIG. 4 along the lateral edges of a fork arm, which weld beads extend over the entire course of the areas to be welded together. However, this involves the outer surfaces of the lamellas, wherein welding them together effects that the welds behave like two upright flat steel bars, as a result of which these upright flat steel bars bend extensively in the load direction, wherein the individual lamellas follow this movement by axially shifting. The static effect of a fork arm structured in this manner corresponds to an equally dimensioned profiled tube, and overall, the desired strength values cannot be achieved.